A novel strategy for modeling composition-/temperature-dependent viscosity in multicomponent melts: Mg-Al-Zn-Sn-Bi as a test case

A viscosity model based on CALPHAD principles, considering the influences of associates in multicomponent melts, was developed. A strategy for determining CALPHAD-type viscosity parameters in systems lacking experimental data was proposed, which combines the Kozlov-Romanov-Petrov model and thermodynamic descriptions. This model and strategy were applied to analyze viscosities in Mg-Al-Zn-Sn-Bi melts. The viscosity expressions of pure melts were initially assessed based on the available experimental data. Subsequently, the Arrhenius viscosities of Mg₃Bi₂, Mg₂Sn, and MgZn₂ associates were determined by integrating thermal-physical properties into Kaptay equation. Viscosity parameters for 10 sub-binary and sub-ternary systems within Mg-Al-Zn-Sn-Bi system were examined. A comparison between predicted and measured viscosities confirmed the accuracy of the model. Isothermal viscosities in all sub-ternary melts were calculated to assess the impact of alloying elements on viscosity. Additionally, viscosities in AZ91 alloys with Bi and Sn additions were predicted, demonstrating an increase in viscosity with higher Bi or Sn content.